Disk-reproduced signal equalizer for use in constant wave length-constant angular velocity scheme

ABSTRACT

A disk-reproduced signal equalizer includes pairs of delay circuits, selection circuits, and a differential amplifier circuit. The delay circuits are arranged in correspondence with a plurality of divided track areas on a disk and respectively having delay characteristics set to provide optimal equalization characteristics, for each track area, with respect to a reproduced signal input from a disk recording/reproducing apparatus of a constant wave length-constant angular velocity scheme of performing a recording/reproducing operation at a substantially constant recording wave length by changing a clock frequency in accordance with a track position while keeping a rotational speed of the disk constant. Each delay circuit has a plurality of output taps. The selection circuits select one of the pairs of delay circuit on the basis of information supplied from the disk recording/reproducing apparatus and indicating a track position. The differential amplifier circuit receives outputs from the output taps of one pair of delay circuit selected from the plurality of pairs of delay circuit, and performs predetermined equalization processing.

BACKGROUND OF THE INVENTION

The present invention relates to a disk-reproduced signal equalizer and,more particularly, to a disk-reproduced signal equalizer applied to adisk recording/reproducing apparatus of a CWL-CAV (Constant WaveLength-Constant Angular Velocity) scheme in which arecording/reproducing operation is performed at an almost constantrecording wave length by changing the clock frequency in accordance witha track position while keeping the rotational speed of a disk constant.

In the recording/reproduction frequency characteristics of a diskrecording/reproducing apparatus, the amplitude of a high-frequencycomponent is generally smaller than that of a low-frequency component.For this reason, a reproduced signal equalizer is arranged on the outputside of a reproduction head to emphasize the high-frequency component ofa reproduced signal.

For example, data recording schemes for disk media include a CAV(Constant Angular Velocity) scheme of recording data at a constant bitrate while keeping the rotational speed of a disk constant, a CLV(Constant Linear Velocity) scheme of recording data at a constant bitrate while keeping the track linear velocity constant by changing therotational speed of a disk in accordance with a track position, and aCWL-CAV (Constant Wave Length-Constant Angular Velocity) scheme ofrecording data at an almost constant wave length by changing therecording clock frequency in accordance with a track position whilekeeping the rotational speed of a disk constant.

In disk recording/reproducing apparatuses of the CAV and CLV schemes,since the bit rate of a reproduced signal is almost constant, and themaximum frequency of the reproduced signal hardly changes, a reproducedsignal equalizer having fixed equalization characteristics is used.

FIG. 3 shows a conventional disk-reproduced signal equalizer applied toa CAV scheme disk recording/reproducing apparatus. An optical head 13 ofthe disk recording/reproducing apparatus reads an analog reproducedsignal S11 of a constant bit rate from an optical disk 11 which isrotated at a constant angular velocity by a disk motor 12. In adisk-reproduced signal equalizer 14, the analog reproduced signal S11 isamplified by a buffer amplifier 141 and is delayed by delay circuits 142and 143, each having a delay time r. The analog reproduced signal S11 isthen input to a differential amplifier circuit 144 via buffer amplifiers145 to 147 and tap gain setting resistors 148 to 150 so as to be outputas an equalized reproduced signal S12 which has undergone predeterminedequalization processing. Letting fp be the emphasized peak frequency ofthe analog reproduced signal S11, fp=1/2τ.

FIG. 4 shows another conventional disk-reproduced signal equalizer. In adisk-reproduced signal equalizer 15, an analog reproduced signal S11from an optical head 13 is amplified by a buffer amplifier 91 and isdigitized by an A-D converter 92. In this case, A-D conversion isexecuted by using a clock signal S13 having a constant period, which issupplied from a clock generator 98. The digitized reproduced signal issubjected to predetermined equalization processing in a knowntransversal filter 97. More specifically, delay circuits 94a to 94doperate in accordance with the clock signal S13 to delay the digitizedreproduced signal by a predetermined time and output the respective tapoutputs to coefficient multipliers 95a to 95e. An adder 96 adds the tapoutputs respectively multiplied by coefficients by the coefficientmultipliers 95a to 95e, and outputs an equalized reproduced signal S22.

In a CWL-CAV scheme disk recording/reproducing apparatus, the bit rateincreases as a head moves toward the outer peripheral side of a disk, sothat the maximum frequency which allows a recording/reproducingoperation increases. For this reason, if the ratio of the peripheralvelocity on the outer peripheral track of a disk to that on the innerperipheral track is large, proper equalization processing is difficultto perform. That is, even if the equalization characteristics areoptimized on the basis of the maximum frequency of a reproduced signalon the inner peripheral track, since the maximum frequency of thereproduced signal on the outer peripheral track increases, predeterminedequalization processing cannot be performed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a disk-reproducedsignal equalizer which is applied to a CWL-CAV scheme diskrecording/reproducing apparatus and designed to perform optimalequalization processing for a reproduced signal whose maximum frequencychanges in accordance with a track position.

In order to achieve the above object, according to the presentinvention, there is provided a disk-reproduced signal equalizercomprising a plurality of pairs of delay means arranged incorrespondence with a plurality of divided track areas on a disk andrespectively having delay characteristics set to provide optimalequalization characteristics, for each track area, with respect to areproduced signal input from a disk recording/reproducing apparatus of aconstant wave length-constant angular velocity scheme of performing arecording/reproducing operation at a substantially constant recordingwave length by changing a clock frequency in accordance with a trackposition while keeping a rotational speed of the disk constant, each ofthe delay means having a plurality of output taps, selection means forselecting one pair of the plurality of pairs of delay means on the basisof information supplied from the disk recording/reproducing apparatusand indicating a track position, and differential amplifier means forreceiving outputs from a plurality of output taps of the one pair ofdelay means selected from the plurality of pairs of delay means, andperforming predetermined equalization processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a disk-reproduced signal equalizeraccording to an embodiment of the present invention;

FIG. 2 is a block diagram showing a disk-reproduced signal equalizeraccording to another embodiment of the present invention;

FIG. 3 is a block diagram showing a conventional disk-reproduced signalequalizer; and

FIG. 4 is a block diagram showing another conventional disk-reproducedsignal equalizer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below with reference to theaccompanying drawings.

FIG. 1 shows a disk-reproduced signal equalizer according to anembodiment of the present invention. The disk-reproduced signalequalizer of the present invention is applied to the following CWL-CAVscheme disk recording/reproducing apparatus. The apparatus uses anoptical disk 101 rotated at a constant angular velocity by a disk motor2 and having upper and lower surfaces on which data can be recorded. Anoptical head 103 arranged at one surface of the optical disk 101 movesfrom the inner periphery to the outer periphery of the optical disk 101,as indicated by an arrow A. An optical head 104 arranged at the othersurface of the optical disk 101 moves from the outer periphery to theinner periphery of the optical disk 101, as indicated by an arrow B.With this arrangement, the sum total of the bit rates of recording datasupplied to the optical heads 103 and 104 is always kept constant. Theoptical heads 103 and 104 respectively output analog reproduced signalsS1 and S2. Track position detectors 105 and 106 respectively outputpieces of track position information P1 and P2.

For example, the track position detectors 105 and 106 may be designed togenerate the pieces of track position information P1 and P2 bymechanically and directly reading the positions of the optical head 103and 104, or to generate the pieces of track position information P1 andP2 by reading track addresses recorded in advance on the optical disk101 for each track. The pieces of track position information P1 and P2are pieces of information indicating the distance from the center of theoptical disk 101 to a target track and are used to perform optical headposition control and generate a recording/reproduction clock in arecording/reproducing operation.

Disk-reproduced signal equalizers 107 and 108 receive the analogreproduced signals S1 and S2 from the optical head 103 and 104 andperform equalization processing to output the resultant signals asequalized reproduced signals S3 and S4, respectively. In this case, eachtrack of the optical disk 101 is divided into three areas, andequalization processing is performed with respect to each reproducedsignal for each track area. Note that since the disk-reproduced signalequalizers 107 and 108 have the same arrangement, the internal blocks ofonly the disk-reproduced signal equalizer 107 are shown in FIG. 1 andwill be described below.

The disk-reproduced signal equalizer 107 includes three pairs ofseries-connected delay circuits (172a and 173a), (172b and 173b), and(172c and 173c) respectively having delay times τa, τb, and τc,selection circuits 174, 175, and 176 for selecting one of the threepairs of series-connected delay circuits, a switching control circuit177 for controlling the selection circuits 174, 175, and 176 inaccordance with the track position information P1, and a differentialamplifier circuit 178.

The analog reproduced signal S1 is amplified first by a buffer amplifier171 and then passes through the three pairs of series-connected delaycircuits (172a and 173a), (172b and 173b), and (172c and 173c). Theselection circuits 174, 175, and 176 respectively tap outputs from thebuffer amplifier 171 and the three pairs of series-connected delaycircuits (172a and 173a), (172b and 173b), and (172c and 173c) via abuffer amplifier 179 and a tap gain setting resistor 180. Each of theselection circuits 174, 175, and 176 is then controlled by the switchingcontrol circuit 177 to select one of the received tap outputs. Thedifferential amplifier circuit 178 receives the three outputs from theselection circuits 174, 175, and 176 and outputs the resultant signal asthe equalized reproduced signal S3 which has undergone predeterminedequalization processing.

In this case, the delay times τa, τb, and τc of the delay circuitsconstituting the three pairs of series-connected delay circuits are setto provide optimal equalization characteristics with respect to each ofthe three divided areas of each track of the optical disk 101. Note thatif each track is divided into n areas (n is an integer of two or more),n pairs of delay circuits may be arranged for the respective trackareas.

As described above, a plurality of pairs of series-connected delaycircuits are arranged in accordance with the respective track areas on adisk, and one of the plurality of pairs of series-connected delaycircuits is selected in accordance with a track position, therebyperforming optimal equalization processing with respect to a reproducedsignal whose maximum frequency changes in accordance with a trackposition. Note that equalization processing with higher precision can berealized by increasing the number of divided track areas.

FIG. 2 shows a disk-reproduced signal equalizer according to anotherembodiment of the present invention.

This embodiment uses a variable frequency oscillator 193 in place of theclock generator 98 of the conventional disk-reproduced signal equalizer15 shown in FIG. 4. The variable frequency oscillator 193 generates aclock signal S6 by changing the frequency in accordance with trackposition information P1. The frequency of the clock signal S6 is set tobe equal to that of a recording clock at a track indicated by the trackposition information P1.

More specifically, a disk-reproduced signal equalizer 109 of thisembodiment is constituted by the variable frequency oscillator 193, abuffer amplifier 191, an A-D converter 192, and a transversal filter197. The variable frequency oscillator 193 generates the clock signal S6by changing the frequency in accordance with the track positioninformation P1. The buffer amplifier 191 amplifies a reproduced signalS1 from the optical head 103. The A-D converter 192 receives the clocksignal S6 from the variable frequency oscillator 193 and A-D-converts anoutput from the buffer amplifier 191. The transversal filter 197receives the clock signal S6 from the variable frequency oscillator 193and performs predetermined equalization processing with respect to anoutput from the A-D converter 192, thereby outputting an equalizedreproduced signal S5. The transversal filter 197 is constituted by aplurality of delay circuits 194a to 194d, coefficient multipliers 195ato 195e, and an adder 196. The delay circuits 194a to 194d areseries-connected and sequentially delay an output from the A-D converter192. The coefficient multipliers 195a to 195e receive and weight tapoutputs from the A-D converter 192 and the delay circuits 194a to 194d.The adder 196 adds outputs from the coefficient multipliers 195a to195e.

The analog reproduced signal S1 from the optical head 103 is amplifiedby the buffer amplifier 191 and input to the A-D converter 192. The A-Dconverter 192 digitizes the analog reproduced signal from the bufferamplifier 191 in accordance with the clock signal S6 from the variablefrequency oscillator 193, and supplies the digital signal to the delaycircuits 194a to 194d constituting the transversal filter 197. The delaycircuits 194a to 194d operate in accordance with the clock signal S6 todelay the digital reproduced signal by a predetermined time and outputthe respective tap outputs to the coefficient multipliers 195a to 195e.The adder 96 adds the tap outputs respectively multiplied bycoefficients by the coefficient multipliers 195a to 195e, and outputsthe resultant signal as the reproduced signal S5 which has undergonepredetermined equalization processing.

With this operation, the delay amounts of the delay circuits 194a to194d for determining the emphasized peak frequency of a reproducedsignal change in accordance with a track position, so that theemphasized peak frequency changes in proportion to the track linearvelocity. Therefore, optimal equalization processing can always beperformed for a reproduced signal.

As has been described above, according to the present invention, in adisk-reproduced signal equalizer applied to a disk recording/reproducingapparatus of the CWL-CAV scheme of recording/reproducing data at analmost constant recording wave length by changing the clock frequency inaccordance with a track position, a plurality of pairs ofseries-connected delay circuits for providing optimal equalizationcharacteristics for a reproduced signal are arranged in correspondencewith the respective track areas on a disk, and one of the plurality ofpairs of series-connected delay circuit is selected in accordance with atrack position. With this operation, optimal equalization processing canbe performed for a reproduced signal whose maximum frequency changes inaccordance with a track position, and an improvement in reproductionquality can be achieved.

In addition, the disk-reproduced signal equalizer may include a variablefrequency oscillator for generating a clock signal whose frequencychanges in accordance with track position information. In thisarrangement, a reproduced signal is digitized in accordance with a clocksignal, and a transversal filter is operated in accordance with thisclock signal. With this operation, optimal equalization processing canbe performed with respect to a reproduced signal whose maximum frequencychanges in accordance with a track position, and an improvement inreproduction quality can be achieved.

What is claimed is:
 1. A disk-reproduced signal equalizer for processinga disk-reproduced signal comprising:a plurality of pairs of delay meansarranged in correspondence with a plurality of divided track areas on adisk and respectively having delay characteristics for each track area,with respect to a reproduced signal input from a diskrecording/reproducing apparatus of a constant wave length-constantangular velocity scheme of performing a recording/reproducing operationat a substantially constant recording wave length by changing a clockfrequency in accordance with a track position while keeping a rotationalspeed of the disk constant, each of said delay means having a pluralityof output taps; selection means for selecting one pair of said pluralityof pairs of delay means on the basis of information supplied from saiddisk recording/reproducing apparatus and indicating a track position;and differential amplifier means for receiving outputs from a pluralityof output taps of said one pair of delay means selected from saidplurality of pairs of delay means, and performing predeterminedequalization processing, whereby the disk-reproduced signal is processedto obtain a desired, optimized equalization characteristic.
 2. Anequalizer according to claim 1, wherein a delay time is set in each ofsaid plurality of pairs of delay means with respect to a maximumfrequency in each track area.
 3. An equalizer according to claim 1,wherein when said disk is divided into n track areas, n pairs of delaymeans are arranged in correspondence with the n tracks.
 4. An equalizeraccording to claim 1, further comprising switching control means forcontrolling a selecting operation of said selection means on the basisof information supplied from said disk recording/reproducing apparatusand indicating a track position.
 5. An equalizer according to claim 1,wherein said differential amplifier means outputs an equalizedreproduced signal having said optimized equalization characteristic withrespect to a maximum frequency in each track area.